1. Field of the Invention
The present invention is generally related to open cycle reactors and more particularly to passive cooling of open cycle reactors.
2. General Background
Open cycle reactors intended for use in outer space have generally been focused on their use in nuclear rockets. Core fission power from delayed neutrons and gamma heating from fission products will continue to produce power after the reactor is shutdown. Information obtained from the NERVA program indicates that, because of this continued heating, the rocket engine turbopump would have to provide coolant to the reactor after reactor shutdown to prevent core melting. This turbopump was powered by coolant heated in the reactor core by decay heat. However, the turbopump could not operate efficiently at the low coolant flows and reactor powers produced by decay heat. This led to an operating scheme where the turbopump would be operated in a pulsed mode. In this mode, the engine is allowed to heat up to the designed operating temperature before providing a burst of coolant flow which would cool the reactor down to a lower temperature. The problem with this mode of operation is that it cycles much of the engine equipment and increases the potential for failure. One approach is to have the coolant pump continue to pump coolant to the reactor at a reduced rate. Pump failure or premature emptying of the coolant tank can result in reactor damage by melting. Over cooling of the reactor can also cause damage if the flow rate of the coolant pump is too high. This leaves a need for a means of removing decay heat from the reactor that does not require constant cycling of the engine equipment and is not dependent on the coolant pump.